This invention relates to a control method and apparatus for a servo-mechanism, and particularly to a control method and apparatus for a servo-mechanism used in a plant or used in a machine tool, magnetic tape memory unit or disk memory unit.
The control system of the above-mentioned servo-mechanism is required to respond quickly and accurately. In order to fulfill these demands, the control system is designed to have characteristics of high sensitivity, and the system is sensitive even to the variation of characteristics of the control object and to disturbances, and consequently the system inherently involves a problem of instability.
A method of dealing with this matter is disclosed in Japanese patent publication JP-A-60-218106. The control system based on this method includes a dynamic model 36 of a control object 1, an output error compensator 37, and subtracters 65 and 66, in addition to a control operator 38 which calculates an operation value U.sub.A from the difference between a desired value R and a control output Y of a control object, as shown in FIG. 12.
In the control system of FIG. 12, the dynamic model 36 receives the desired value R and produces an output Y.sub.M which represents a control output based on the assumption that the control object 1 does not vary in characteristics and the system is not subjected to disturbances. Accordingly, the difference E between the output Y.sub.M of the dynamic model 36 and the actual control output Y of the control object 1, as evaluated by the subtracter 66, is assumed to be attributable to the variation of characteristics of the control object and the variation of the control output caused by disturbances D. The output error Compensator 37 converts the difference E into a variation component Uc of the operation value Y due to variations in characteristics and disturbances, and the subtracter 65 subtracts the value Uc from the calculated operation value U.sub.A thereby to produce a modified operation value U.
Since the modified operation value U is rid of the variation component Uc caused by the variation of characteristics of the control object and disturbances, the control system is less sensitive to the variation of characteristics of the control object and disturbances, while it is highly responsive to the variation of desired value R, and the control system can be stabilized.
A similar technique is disclosed in JP-A-3-63704.
However, these conventional control systems necessitate a complex output error compensator when it is intended to compensate the operation value against wide variations of characteristics of the control object.
Further, for example, the arrangement of FIG. 12 excluding the control object 1 and dynamic model 36 is not much dependent on the control object, and it is desirably of common design for a variety of control objects. In addition, such an arrangement is based on accumulation of knowledge and know how in design, and thus it is desirable to use it in common with different control objects. In this respect, the control system of the patent publication JP-A-60-218106 supplies the dynamic model 36 with the desired value R for its input, and therefore it is not suited to standardize the controller for a variety of control objects merely by attaching a control object to the common control portion. On the other hand, in order to comprehend the variation of characteristics among control objects, it is desirable to calculate the model-based control output which is closely associated with the control object.